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How does the temperature affect the plant growth?

How does the temperature affect the plant growth?

Question 1: How does the temperature affect the plant growth?

Question 2: How does the soil temperature affect seed germination?

Introduction: (Initial Observation)

For farmers and growers it is important to know the best conditions for the growth of their products. In the past, just by experience most farmers and growers learned what is the best season for planting certain plants. With modern technologies and production of plants in green houses and other controlled environments, we have lost part of our dependencies to seasons and weather conditions. We now need to know the best conditions and adjust our environment according to that. Temperature, light, air, water, soil, pH and nutrients are among the factors that may be studied for each specific plant.

In this project you will attempt to identify the effect of temperature on the growth of a specific plant of your choice.

To ensure using same age plants for your experiment, you may choose to start by planting seeds.

Please note that this project guide covers two similar projects.

Question 1: How does the temperature affect the plant growth?

Question 2: How does the soil temperature affect seed germination?

Be careful not to mix up related experiments.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor


Plant growth is not the only variable that is affected by the temperature. Often researchers are interested to know how temperature affects the formation of certain vitamins or other chemical compounds in plants. Also, when studying the effect of temperature, you may test the effect of temperature in root zone or the effect of temperature on a plants body.

Information Gathering:

Find out about the factors that affect plant growth. Read books, magazines or ask professionals who might know in order to learn about the possible methods that you can use to test the effect of different factors on plant growth. Keep track of where you got your information from.

The following are samples of information that you may gather.

What plant can I use for my experiments?

You have a large variety of choices. It is good to start from planting seeds or using small and young plants. It is easier to detect the growth in small plants than larger ones.

Another benefit of planting seeds is that all your plants will have the same age.

How do I determine plant growth?

The most common method for students to determine plant growth is measuring the plant height. In more advanced methods, researchers may count the number of leaves, measure the size of leaves or measure the total biomass of the plants after completion of the experiments. Total biomass is the weight of dry plant including roots, stem and leaves. This method requires oven to dry up the plant and high precision scale to weigh the dried plant.

Effect of temperature on plants


Temperature influences most plant processes, including photosynthesis, transpiration, respiration, germination, and flowering. As temperature increases (up to a point), photosynthesis, transpiration, and respiration increase. When combined with day-length, temperature also affects the change from vegetative (leafy) to reproductive (flowering) growth. Depending on the situation and the specific plant, the effect of temperature can either speed up or slow down this transition.


The temperature required for germination varies by species. Generally, cool-season crops (e.g., spinach, radish, and lettuce) germinate best at 55°F to 65°F, while warm-season crops (e.g., tomato, petunia, and lobelia) germinate best at 65° to 75°F.


Sometimes horticulturists use temperature in combination with day length to manipulate flowering. For example, a Christmas cactus forms flowers as a result of short days and low temperatures. To encourage a Christmas cactus to bloom, place it in a room with more than 12 hours of darkness each day and a temperature of 50° to 55°F until flower buds form.

If temperatures are high and days are long, cool-season crops such as spinach will flower (bolt). However, if temperatures are too cool, fruit will not set on warm-season crops such as tomatoes.

Crop quality

Low temperatures reduce energy use and increase sugar storage. Thus, leaving crops such as ripe winter squash on the vine during cool, fall nights, which increases their sweetness.

Adverse temperatures, however, cause stunted growth and poor-quality vegetables. For example, high temperatures cause bitter lettuce.

Photosynthesis and respiration

Thermoperiod refers to daily temperature change. Plants grow best when daytime temperature is about 10 to 15 degrees higher than nighttime temperature. Under these conditions, plants photosynthesize (build up) and respire (break down) during optimum daytime temperatures and then curtail respiration at night. However, not all plants grow best under the same range between nighttime and daytime temperatures. For example, snapdragons grow best at nighttime temperatures of 55°F; poinsettias, at 62°F.

Temperatures higher than needed increase respiration, sometimes above the rate of photosynthesis. Thus, photosynthates are used faster than they are produced. For growth to occur, photosynthesis must be greater than respiration.

Daytime temperatures that are too low often produce poor growth by slowing down photosynthesis. The result is reduced yield (i.e., fruit or grain production).

In one research, effect of root zone temperature on plant growth (greenhouse) are experimented and produced the results shown in the right picture.

Temperatures are Celsius degrees.

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Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement. The following is a sample:

For Question 1:

The purpose of this project is to determine how temperature affects plant growth. The results of such research can help a grower to identify the best temperature for optimizing the growth of any specific plant.

For Question 2:

The purpose of this project is to see in which soil temperature (32°c, 18°c or 5°c) more seeds will sprout.

The information gained from this research could be used to help gardeners determine the best soil temperature for one specific plant.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

For question 1:

  • Independent variable (also known as manipulated variable) is the soil temperature.
  • Dependent variable (also known as responding variable) is the rate of plant growth.
  • Controlled variable is the amount and type of light and air.
  • Constants are: Plant type, initial plant age/ size, type and amount of soil, type size and shape of pot, amount of water, frequency of watering.

For question 2:

  • Independent variable is the soil temperature.
  • Dependent variables are the speed of germination and the rate of seed germination.
  • Controlled variables are: Nothing!, I don’t know of any other environmental factor that may affect the rate of seeds that sprout.
  • Constants are: Type and number of plant seeds, type of soil, amount of water, frequency of watering, type and size of pots, type of seeds.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following are two sample hypothesis:

For question 1:

Plants grow best at higher temperatures if they have sufficient or unlimited supply of water.

My hypothesis is based on my observation of plants in different seasons. I have noticed that more plants grow in summer time while only a few can survive the winter.

For question 2:

My hypothesis is that the seeds with the  soil temperature 18ºC will sprout faster and at a higher rate than the seeds with the soil temperature higher and lower.

I base my hypothesis based on Encarta 2000, which says extreme cold, or heat will make the plant unable to be germinated. I also based it on my mom as a plant grower she said that when she put plants next to a heater they needed more water more often then the other plants in the house and if the plant did not have the extra water they would start to die.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: How does the temperature affect the plant growth?

Introduction: In this project I will grow three groups of identical young plants at three different temperatures. For each group or each temperature I will use three plants to make sure that my results will not be accidental. To create different temperatures, I will perform my experiments in a very cold room under artificial light, so I will be able to use a small electric heater to make variations of heat that I need.

Procedure part 1: (If you are starting from seeds)

  1. Get 12 identical small pots and fill them up with potting soil
  2. Use your finger or a pencil to make two holes about 1 inch deep in each pot. Drop one seed in each hole and cover the seeds with potting soil. (As a seed I usually use some kind of beans that I usually have at home. You can use any type of seeds that you like. Instead of potting soil, you may use any other soil that can keep enough moisture or you may use some potting soil with some top soil.)
    Water all 12 pots and keep them at room temperature. A warm room is preferred. No light is required at this stage until the seeds sprout.
  3. Continue watering your seeds every day to make sure that the soil will remain moist. (Not soaked). Depending on the type of seeds, they may germinate in about 10 to 20 days. (For most seeds it is helpful if you soak them in water for 24 hours prior to planting them in the soil)
  4. When your young plants are ready or if you are purchasing identical young plants, go to procedure part 2.

Procedure part 2: Testing the effect of temperature

  1. Divide your young plants in 4 groups. Label them “Cold”, “Medium”, “Warm”, “Very warm”. (Note that you could have more pots and more groups. For example you could have another group called hot or very hot. Or you could classify your groups based on temperature range such as 51ºF-60ºF, 61ºF-70ºF, 71ºF-80ºF,…)
  2. Surround each group with a box. Put a glass or Plexiglas on the top of each box so the light can go through. Make some holes at the lower part of each box so the air can flow.
  3. Place identical fluorescent lights (or compact fluorescent lights) above each box.
  4. For groups medium, warm and very warm use one electric heater. Very warm is closest to the heater, warm is the next and medium is the third.
  5. Place one thermometer on each pot so you can read the temperature. Move the boxes or groups closer or further from the heater to maintain the proper temperature range that you expect.
  6. Water all plants with identical amounts of water every day. Make daily observations of growth and conditions of each plant.
  7. After 2 or 3 weeks remove the heater and lights and make your final observation by recording your final data. General plant condition and the plant height are two important factors that you may record. The following is a sample results table:

Plants condition and growth in different temperatures for 14 days

Plant Number Plant Group Initial height Final Height General Condition
1 Cold
2 Cold
3 Cold
4 medium
…. …..

Your table will have 12 rows of results unless you are using a different number of plants. Your results table may optionally contain more information about each plant. Number of leaves and the size of the largest leaf in each plant before and after the experiment are among the additional information that you may want to include.

Summarize your results table by calculating the average plant height for each group and make a new results table like this:

Plants condition and growth in different temperatures for 14 days

Plant Group Initial height Final Height General Condition
very warm

Use the above results table to draw a bar graph. Use one bar for each temperature group. The height of bar can be the same as the plant height at the end of your experiment.

Additional Notes: You may do this experiment in many different ways. For example you may place each group in a different place in your house with a different temperature range. In this way you will not need an electric heater. The only thing that you must be careful about is that all your plants should get the same amount of light, water, air and nutrients. The only difference must be in temperature.

Experiment 2: How does the soil temperature affect seed germination?

Introduction: Temperature may also affect the speed and rate of germination in seeds. In this experiment seed germination will be tested at different temperatures.


  1. Gather Materials.
  2. Take scissors and cut open a bag of potting soil.
  3. Put 3/4 cup of potting soil in pots
  4. Put one seed in each pot.
  5. Put remaining 1/4 cup of potting soil over seeds
  6. Label the pots as A, B, C, D, E and F
  7. Place pots A and B over a heating source such as a radiator.
  8. Keep pots C and D at room temperature, away from heat source.
  9. Place pots E and F in a cold place such as a refrigerator.
  10. Check all the pots every morning and every night around the same time. Look for any sprouts.
  11. Water plants/ pots every two days. Water enough to keep the soil moist, not soaking wet. Also use the same amount of water for all pots. Excess water may drain from a hole at the bottom of each pot.
  12. When plants sprout, record data.
  13. Your data table will look like this:
Cold Medium Warm
Start date
Sprout date

Materials and Equipment:

List of material depend on your final experiment design. You must make your own list of material.

This is a sample list of material for experiment number 2:

  1. 6 Flower Pots
  2. 6 Seeds
  3. 1 Bag of Potting Soil
  4. 1 Heating Source
  5. Water
  6. 1 Pair of Scissors
  7. 1 Thermometer

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

This is a sample result for experiment number 2:

The original purpose of this experiment was to see in which soil temperature (32°c, 18°c or 5°c) more seeds will sprout.

The results of the experiment showed that A and B sprouted faster then the other four by one day.

Note that your results may be different. Never rely on the results of experiments performed by other students.


For experiment number 1, you will need to calculate the average plant height in each group.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed  numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Following is a sample conclusion for experiment number 2:

My hypothesis was that the plant with the soil temperature “normal” would sprout faster then the plant with the soil temperature “higher” or “lower”.

The results indicate that this hypothesis should be rejected. Do to seeds A and B sprouting faster then my hypothesis which was plants C and D.

Because of the results of this experiment, I wonder if more heat was to be added to plant A and B if they would still sprout faster then the others.

If I were to conduct this project again I would have used many more plants than just two in each category. Also I would have waited till the plant reached a growth of five inches. So I could see if some plants died off after sprouting.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


Visit your local library and find books related to botany and plant biology.

After you complete your experiments and draw a conclusion, compile a report about your project. Following is a sample:



Have you ever put a plant by heater and the plant died or you put a plant in the garage in winter and it never sprouted? Have you ever wondered which temperature a plant grows best in?
This experiment is to find out in which plants grow best.
This report contains information on Seed Germination, Seed Dormancy, Root (botany) and Stems and Leaves.

Seed Germination

Germination dose not take place unless the seed is in a good environment the main keys for growing a plant are adequate water and oxygen and also sunlight. Different kinds of plant germinate at different temperatures. Some plants require more sunlight to germinate then others. During germination, water diffuses though the seed coats into the embryo, which has been almost completely dry during the period of dormancy. With the absorption of oxygen by the seed, energy is made available for growth. From the time of germination until the plant is completely independent of food stored in the seed, the plant is known as a seedling.

Seed Dormancy

Seed Dormancy is when a seed has fallen form the parent plant before they are able to germinate. Lack of viability of seed is often confused with seed dormancy. Many seeds require a so-called resting period after the have fallen from there parent plant. In some plants, chemical changes take place during the resting period that make the seed ready for germination. Still other seeds have extremely tough seed coats that must soften or decay before water and oxygen can enter the seed to take part in the growth of the embryo, or before the growing embryo is capable of bursting through the seed coat.

Root (botany)

The first root of the plant, known as the radicle, elongates during germination of the seed and forms the primary root. Roots that branch from the primary root are called secondary roots. In many plants the primary root is known as a taproot because it is much larger than secondary roots and penetrates deeper into the soil. Some plants having taproots cannot be transplanted easily, for breaking the taproot may result in the loss of most of the root system and cause the death of the plant.

Stems and Leaves

Stems usually are above ground, grow upward, and bear leaves, which are attached in a regular pattern at nodes along the stem. The portions of the stem between nodes are called internodes. Growing plants give rise to new leaves, which surround and protect the stem tip, before they expand. Stems are more variable in external appearance and internal structure than roots, but they also consist of three tissue systems and have several features in common.
Leaves are the primary photosynthetic organs of most plants. They usually are flattened blades that consist, internally, mostly of parenchyma tissue called the mesophyll, which is made up of loosely arranged cells with spaces between them. The spaces are filled with air, from which the cells absorb carbon dioxide and into they expel oxygen. The leaf blade is connected to the stem though a narrowed portion called the petiole, or stalk, which consists mostly of vascular tissue.


This report explained about seed germination. The term seed germination is applied to the resumption of the growth of the seed embryo after the period of dormancy. This report also talks about seed dormancy, which is when a seed has fallen form the parent plant before they are able to germinate. This report also talks about root (botany). Which tells about the roots of the plants. This report also talks about stems and leaves. Stems are usually above ground, grow upward and bear leaves. Leaves are primary photosynthetic organs of most plants.


“Germination”, Encarta 1998. CD-ROM. 1998
“Seed Germination”, Encarta 1999. CD-ROM. 1999
“Germination”, Encarta 2000. CD-ROM. 2000
“Root (Botany)”, Encarta 2000. CD-ROM. 2000
“Stems”, Encarta 2000. CD-ROM. 2000
“Leaves”, Encarta 2000. CD-ROM. 2000
Keating Richard C., “Germination”, The World Book Encyclopedia. 1998, 173